My favourite was always 66-0166, don't know why, it wasn't the first I ever saw - my older spotting mate got an airband in '76 and we saw four on 3rd September 1976 - next day was the Battle of Britain show at Biggin, which is why I remember - got my own airband a year or two later and I recall the excitement of hearing my first C-5 call up - first I ever saw!
Looking at my dusty old mil log, I never did see 64-0612 though I probably saw rather more than half of the C-141 fleet. I remember seeing six pass over one morning during the Easter holidays, either Strumble/Woodley/Dover or Lands End/Midhurst/Dover...